Pre-clinical studies of bone regeneration with human bone marrow stromal cells and biphasic calcium phosphate

Introduction: Repair of large bone defects remains a significant clinical challenge. Bone marrow stromal cells (BMSCs), a subset of which is known as bone marrow-derived mesenchymal stem cells, show therapeutic potential for bone regeneration. However, their isolation, expansion and implantation will need to be conducted under good manufacturing practices (GMP) at separate locations. An investigation which mimics this clinical scenario where large bone defects shall be regenerated is required before clinical trials can be initiated. Methods: Seven batches of 100 million human ex-vivo expanded BMSCs from five donors were transported fresh in syringes from a GMP facility in Germany to France. BMSCs were mixed with biphasic calcium phosphate (BCP) biomaterial prior to subcutaneous implantation in nude mice. The capacity of BMSCs in unison with BCP to regenerate critical sized cranial bone defects was also evaluated. BMSCs expressing luciferase were used to assess the viability and bio-distribution of implanted cells. In situ hybridization, using the human-specific repetitive Alu sequence, was performed for the identification of human cells in explants. Results: Eight weeks after implantation of BMSCs, mineralized bone containing mature bone marrow territories was formed in ectopic sites and in calvaria defects. Significant loss of cell viability was observed by bioluminescence imaging and only 1.5 percent of the initial number of transplanted cells remained after 37 days. After eight weeks, while explants were comprised primarily of host cells, there were also human cells attached along the periphery of BCP and embedded in osteocyte lacunae dispersed throughout the newly formed bone matrix. Conclusions: This study demonstrates the safety and efficacy of BMSC/BCP combinations and provides crucial information for the implementation of BMSC therapy for bone regeneration.